Low frequency noise generator



April 23, 1968 c. G. DORN 3,379,996

LOW FREQUENCY NOISE GENERATOR Filed Dec. 6, 1966 Io l 24 23 I o o o o 0';

MOTOR fi 8O (%O8O9O88O- 4 DRIvE I 122 w so AMPLIFIER 34 FILTER AND FIG. CLIPPER IO\ I2 20 O OO/ 05 23 O0 000 00 MOTOR liq 52 ;OOOOOOQOOQO O- [50 A? DRIvE AMPLIFIER AMPLIFIER 5| FILTER AND FILTER AND 0 CLIPPER CLIPPER CLIFFORD G. DORN INVENTOR.

A BY United States Patent 3,379,996 LOW FREQUENCY NOISE GENERATOR Ciiiford G. Dorn, Riverside, Califi, assignor to the United States of America as represented by the Secretary of the Navy Filed Dec. 6, 1966, Ser. No. 600,002 5 Claims. (Cl. 331-48) ABSTRACT 0F THE DISCLOSURE An apparatus for producing low frequency noise which is composed of continuous frequency components from DC to one kHz. The apparatus consists of a slowly rotating container partially filled with ball bearings which provides a randomly varying resistance path to a voltage applied to conducting shafts in contact with the ball bearings.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to electrical noise or random wave generators. Prior known devices for generating random noise utilized electric discharge tubes in the presence of a magnetic field. The electrical noise present at the low frequencies was a small percentage of the total noise spectrum, Accordingly, an object of the present invention is to provide a low frequency noise generator which is simple in construction and provides low frequency noise at useable power levels.

FIG. 1 is a diagrammatic view of one embodiment of the invention.

FIG. 2 is a diagrammatic view of another embodiment of the invention.

Referring now to the drawing there is shown in FIG. 1 a container made of any good conducting material filled approximately two-thirds full With steel balls 12. Container 10 is suspended on a shaft 14 which is made of a conducting material and extends through container 10 and is in contact with some of the steel balls 12. Shaft 14 is coupled by means of an insulating coupling to the shaft 18 of a motor drive 20. Shaft 14 is supported on one end by motor drive 20 and on the other end by bearing 21 mounted in support member 23. The member 24 enclosing the ends of container 10 is made of any suitable insulating material which has a sufficient weight bearing capacity. Electrical energy is supplied at terminal 26 through current limiting resistor 28 to sliding contact 22 and to an amplifier filter and clipper circuit 30. Container 10 is kept at ground potential through sliding contact 32.

In operation, container 10 is driven slowly (three rpm. has been found to be satisfactory) by motor drive 20 which causes balls 12 to turn and slide and vary in the amount of surface contact to other balls, shaft 14 and the container 10. The electrical resistance to ground varies allowing more or less current to flow from terminal 26 through resistor 28. This changes the voltage applied to amplifier, filter, and clipper 30 and this varies the output at terminal 34.

In FIG. 2 there is shown a modification which supplies two independent, uncorrelated noise voltages at terminals 49 and 51 (FIG. 2). As shown in FIG. 2, container 10 is mounted on two shafts and 52. There are then two current paths from terminal 54 to ground; limiting resistor 56, brush 58, shaft 50, balls 12, container 10 and brush 32, and limiting resistor 6!), brush 62, shaft 52, balls 12, container 10, and brush 32. Amplifier, filter, and clipper 30 are provided to obtain various bandwidth of low frequency noise at useable power levels depending upon what use is to be made of the output signal.

Motor drive 20 may be driven at various speeds and container 10 may be separated int-o many insulated segments which are connected to outputs by sliding contacts. Various numbers and sizes of steel balls 12 may be used and container 10 may be filled to different levels with steel balls.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A low frequency noise generator comprising:

(a) a source of direct current voltage,

(b) a slowly rotating container partially filled with a plurality of moving electrical conducting pieces connected across said direct current voltage for providing a randomly varying resistance,

(c) filter circuit means coupled to said slowly rotating container for producing low frequency noise at a predetermined bandwidth.

2. The low frequency noise generator of claim 1 wherein said electrical conducting pieces are steel balls.

3. The low frequency noise generator of claim 1 wherein said normally randomly varying resistance means includes:

(a) a hollow cylinder made of electrical conducting material enclosed on each end with insulating material,

(b) electrical conducting shaft means extending along the axial axis and extending beyond the ends of said cylinder,

(0) a plurality of steel balls partially fillin g said cylinder and making electrical contact with said shaft means,

(d) and drive means coupled to said shaft means for slowly rotating said cylinder.

4. The low frequency noise generator of claim 3 wherein said shaft means is one continuous shaft.

5. The low frequency noise generator of claim 3 wherein said shaft means comprises two portions electrically separated within said cylinder to provide two electrical conducting paths between said portions, said steel balls and said cylinder.

References Cited UNITED STATES PATENTS JOHN KOMINSKI, Primary Examiner. 

